Micro-fluid ejection devices such as ink jet printers continue to experience wide acceptance as economical replacements for laser printers. Micro-fluid ejection devices also are finding wide application in other fields such as in the medical, chemical, and mechanical fields. As the capabilities of micro-fluid ejection devices are increased to provide higher ejection rates, the ejection heads, which are the primary components of micro-fluid ejection devices, continue to evolve and become larger, more complex, and more costly to manufacture.
One significant obstacle to be overcome in micro-fluid ejection head manufacturing processes is maintaining the position and alignment of the ejection device substrate, also referred to as the ejection chip, and the nozzle plate during and after the manufacturing process, particularly when manufacturing ejection heads having an ejection swath dimension of greater than about 2.5 centimeters. The position and alignment of the ejection chip and the nozzle plate determine the direction in which a fluid such as ink is dispensed.
The position and alignment of the micro-fluid ejection head components may be affected by significant mismatches in coefficients of thermal expansion (“CTE”) between the various members of the ejection head, including the nozzle plate, the device substrate, the base support, and any adhesive material used in securing the aforementioned components to one another.
Current manufacturing processes may utilize an adhesive die-bonding material to secure the device substrate of the ejection head to a support material. However, such adhesive requires thermal curing which may cause expansion and contraction of the components and may lead to warping or bowing of the ejection device substrate and the nozzle plate. Alterations in the thickness of the adhesive layer or the thickness of the underlying support material have led to only marginal improvements in the planarity of the finished devices. However, current manufacturing processes are limited by the size of the ejection chip. As the demand for larger ejection chips having larger ejection swaths increases, new device construction methods may be required to meet high tolerance manufacturing criteria for such ejection heads.
Accordingly, there is a need for improved structures and methods for making substantially planar micro-fluid ejection heads, suitable for ejection chips having an ejection swath dimension of greater than about 2.5 centimeters.
With regard to the above and other objects, the present disclosure is directed to a micro-fluid ejection head having a device substrate with a first surface and a second surface opposite the first surface. At least one fluid flow slot is formed therein from the first surface to the second surface. At least one micro-fluid ejection actuator is adjacent to the second surface. The first surface of the device substrate is hermetically sealed using a basic solution to a support material having at least one fluid flow slot formed therein. The slot in the support is associated with the fluid flow slot in the device substrate. The first surface of the device substrate may be non-planar. One or more of the surfaces of the support may also be non-planar. Both the substrate and the support may comprise silicon, with at least one of the substrate and the support being substantially composed of silicon.
In another aspect of the present disclosure, a process for making a substantially planar micro-fluid ejection head is provided. The process includes depositing a basic solution on a first surface of a device substrate sufficient to wet the first surface of the device substrate. The device substrate has at least one fluid flow channel slot therein and at least one micro-fluid ejection device formed adjacent to a second surface thereof. Next, the wetted surface is contacted together with a surface of a support material for a duration ranging from about 1 minute to about 15 minutes at temperature ranging from about 20° C. to about 90° C., thereby hermetically sealing the support and the device substrate to one another. Both the support and the device substrate may comprise silicon, and at least one of the support and the device substrate may be composed substantially of silicon.
In another embodiment of the present disclosure, a method of bonding a first substrate to a second substrate is provided. The method includes wetting a surface of the first substrate with an aqueous solution of tetramethylammonium hydroxide (TMAH). The wetted surface of the first substrate is contacted to a surface of the second substrate. Both the first substrate and the second substrate may be selected from the group consisting of silicon substrates and substrates containing a silicon oxynitride, silicon carbide, silicon oxide or silicon nitride layer adjacent to the TMAH solution. In some embodiments, only one of the first and second substrates may be wetted with TMAH prior to bonding, while in other embodiments, both substrates may be wetted with TMAH prior to bonding.
A further embodiment of the present disclosure provides a silicon device made by the methods described herein.
Another aspect of the present disclosure provides a method for bonding a first substrate to a second substrate. The method includes applying a silicon-containing basic solution to a surface of the first substrate. The surface having the solution deposited thereon may be contacted together with a surface of the second substrate for a period of time ranging from about 1 minute to about 15 minutes, at a temperature ranging from about 20° C. to about 90° C., with a pressure ranging from about 1 psi to about 50 psi. The method may be performed under an atmosphere selected from the group consisting of hydrogen gas and a hydrogen-containing forming gas. The surfaces having the solution deposited thereon may comprise silicon.
Still another aspect of the present disclosure provides a substantially unitary device structure. The structure may comprise a first substrate, a layer of silicate glass, and a second substrate. The layer of silicate glass may be interposed between the first substrate and the second substrate, and may form a hermetic seal between a surface of the first substrate and a surface of the second substrate. The surface of the first substrate adjacent the layer of silicate glass and the surface of the second substrate adjacent the layer of silicate glass may comprise silicon.
An advantage of the structures and method of the present disclosure is that bond may be formed at a relatively low temperature, thus eliminating heat curing steps of the presently used die-bonding adhesive methods that may result in bowing or warping of the device substrate and nozzle plate due to CTE mismatch between the different materials. In the presently disclosed structure and method, a thinner silicon wafer may be used for the device substrate than with conventional manufacturing techniques, thereby providing a reduction in materials cost for producing micro-fluid ejection devices. Another advantage of the present disclosure is that a covalent bond between the device substrate and the support material provides a hermetic seal that is not susceptible to attack or degradation by fluids such as ink, unlike adhesive die-bonding materials.